A magnet roll employed as a developing roll in electrophotography, electrostatic recording, etc. is circumferentially provided with a plurality of magnetic poles and a non-magnetized portion, that is, a demagnetized pole. The position, number, size and shape of the magnetic poles for a magnet roll depend on the specifications of developer to be attracted and electrophotographic device and the like.
For example, Japanese Patent Application Laid-Open Publication No. 2003-100511 discloses a magnet roll that is integrally formed to have a circular cross-section with a partial cut-away demagnetized pole, that is, a C-shaped cross-section.
Japanese Patent Application Laid-Open Publication No. 2002-43119 discloses a magnet roll that is made up of a plurality of bar magnets to have a profiled cross-section in order to obtain a desired magnetic waveform.